Virtual Embryology Tour: The Egg

Immediately after each follicle is aspirated by the physician, the contents of the follicle are placed on a warmed stage under a microscope where the embryologists search through the follicular fluid for the eggs. Approximately 80% of all eggs retrieved are mature and are capable of being fertilized.

Mature eggs are surrounded by a large number of small cells referred to as the corona radiata. An outer membrane, the zona pellucida, also surrounds the egg. The inside of the egg contains the nucleus and cytoplasm with a large number of organelles, which regulate egg maturation and the very complex cascade of events involved with fertilization and early embryonic development. The picture above represents a mature egg with the outer cells removed. Egg maturity is evidenced by the polar body, which contains half of the egg's DNA, located at the 9 o'clock position.

After retrieval, the mature eggs are given approximately 4 hours to rest before insemination with sperm either through standard in-vitro fertilization or intracytoplasmic sperm injection (ICSI). The oocytes are then placed in incubators and checked daily for growth.